Page 165 - The Building Conservation Directory 2013

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4.2
Services & Treatment : Heating & Lighting Services
Comfort conditions
Heat is transferred by conduction (from the
heat source to a body in contact with it),
radiation (from the heat source to another
body or surface without heating the medium
in between) and convection (from the heat
source to the surroundings through the
mixing of heated air). Radiation is a major
influence on comfort in buildings with
exposed internal masonry surfaces. Occupants
lose heat by radiation to the surrounding
cold stonework of a building. Even during
periods of warm weather when the internal air
temperature in spaces is higher, occupants can
feel cold due to the cold radiation effect. This
heat transferred by radiation does not heat the
air; heat is exchanged between the body and
surrounding surfaces. Under these conditions
the occupants are often more tolerant of lower
internal air temperatures with higher air
leakage when the surface temperatures of the
building envelope are higher.
The diagrams below show the mechanisms
affecting comfort involved.
The mechanisms to maintain thermal
comfort these can be summarised as:
• occupant clothing
• occupant activity
• air temperature
• surface temperatures (radiant effects)
• air movement (drafts)
• humidity (impacts on the ability to sweat).
The combination of these mechanisms will
dictate whether occupants are comfortable.
Comfort is very subjective and normally
conditions are said to be comfortable if 80 per
cent of the occupants have that view.
Usually it is comfort conditions in the
cold winter months that are of concern, but
occasionally where historic buildings are
used for offices, high levels of occupancy and
associated IT equipment can result in high
internal summertime temperatures.
Energy consumption
While considering energy consumption, we
have assumed that only heating is provided
to the building since comfort cooling or air
conditioning are only rarely used in historic
buildings.
Energy consumption will be influenced by
the following factors:
• the relative importance of conservation of
the building/contents and occupant comfort
• activity within the space and
comfort levels expected
• hours of use
• thermal performance of the building
fabric including airtightness
• volume/scale of the spaces being heated
• efficiency and mode of heating
distribution to the building
• efficiency of the heating energy source
• heating control including
management by the occupants.
Approaches to heating
historic buildings
(a) Conservation trust property
This class of building primarily consists of
‘show spaces’ with significant fabric such
as wallpaper, curtains and other valuable
furnishings. Conservation of the fabric and
objects is the primary focus.
Conservation heating is provided to
show spaces to maintain suitable RH levels.
Low internal temperature in winter to show
spaces with associated poor occupant comfort
is acceptable but adequate humidity levels
are maintained for conservation. Ideally
offices and rest rooms where good occupant
comfort are required should be located in
less sensitive areas of the building where the
provision of heating is likely to cause less
risk to fabric. These spaces should be limited
in area and, where possible, have improved
fabric performance. The provision of separate
heating systems for show spaces and back-of-
house should be provided due to the different
demands/output requirements.
Mechanisms affecting comfort: Even though the air temperature may be appropriate, adjacent
cold surfaces such as walls, windows and floors act like cold ‘radiators’. Their effect depends
on their surface temperature, area and distance from the occupant. This radiant effect is
similar to the exposure of a body to direct sunlight. At the same air temperature, a person
exposed to direct solar radiation will be far less comfortable than a person in the shade.
Liverpool Cathedral has recently undertaken
improvements to the heating system to provide
enhanced comfort conditions at events held in the
winter months. An original underfloor labyrinth
system which had not been used since the 1950s was
brought back into operation.
Remains of a Roman heating system in Chester which used the radiant effect of warm walls and floors to heat
‘leaky’ and poorly insulated buildings. Probably the first services engineers, much can be learned from Roman
approaches to providing comfort conditions in historic buildings.